1. Field of the Invention
The invention relates to a process for decarburizing steel melts in a closed metallurgical vessel that is attached to a vacuum unit and into which oxygen is fed via a lance and combustible material is fed via a feed device. The invention also relates to a hollow device for implementing this process.
2. Description of the Prior Art
In what is known as "forced decarburization," oxygen is added during the decarburization phase. The addition of oxygen is always necessary when the oxygen present in the steel is insufficient for decarburization or is so low that the required C removal is not completed in the available time. In processes of this type, for example, immersion tubes of an RH vessel are submerged into the melt. When pressure reduction begins in the RH vessel, the decarburization process begins simultaneously as a function of the pressure reduction. When a low pressure of p&lt;100 mbar is reached, through a hollow oxygen lance O.sub.2 is blown for approximately 1 to 3 minutes. During the deep vacuum phase, self-decarburization takes place; after deoxidation, decarburization is ended.
During decarburization, up to 70% CO is formed. Part of this gas automatically reacts with part of the added oxygen to form CO.sub.2. The degree of post-combustion in this method is less than 30%.
Moreover, it is also a metallurgical practice to add aluminum for the purpose of chemically heating steel melts in atmospheric units. During such chemical heating, the energy gained from the combustion of the aluminum with the added oxygen is used to heat the melt.
In addition to its use in purely thermal heating, aluminum may also be used with other substances to treat the melt. For example, EP 0 110 809 discloses a process for treating steel in a ladle with reactive slags. This process calls for a metal-thermal reaction, whereby oxygen is blown through a lance into a bell submerged in the melt. Combustible metal substances react and, as reactive slags form, a neutral or reductive flush gas is blown in below the tube in which the steel treatment occurs.
The disadvantage of this process, which is used for the desulphurization, deoxidation and purification reaction of steel melts, is the formation of reactive slags, that are created in the bell submerged into the molten metal.
Further, EP 0 347 884 B1 discloses a process for the degasification and desulphurization of molten steel, wherein steel is fed through a container into a vacuum chamber. Arranged in the vacuum chamber at a given distance is an oxygen lance, from which oxygen or a gas containing oxygen is blown in for the purpose of combusting the CO in the surface region of the molten steel located in the vacuum chamber. An amount of oxygen fed through the lance is in accordance with a predetermined ratio of (CO+CO.sub.2)/waste gas quantity or CO/(CO+CO.sub.2),.
From this process, it is not possible to derive the chemical heating of the melt under particular pressure conditions and the blowing in of a defined quantity of surplus oxygen.